Add "info" GRPC request

[MatthiasReumann]

Description

A call to voice.SubtitleGenerator.Info (There certainly is a better name for this endpoint) might return the following object as example:

{
    "transcriber": "vosk",
    "models": ["vosk-model-small-en-us-0.15", "vosk-model-small-de-0.15"],
    "languages": ["en", "de"],
    "receiver": "::50055"
}

Why?

Such an endpoint could make debugging already deployed services a bit less gruesome.